Understanding the biology of the Wichita Mountains pillsnail, Euchemotrema wichitorum, and related species in western Oklahoma

Abstract

The Wichita Mountains pillsnail, Euchemotrema wichitorum, was originally described in 1972 from surveys in two counties in southwest Oklahoma. Virtually all that was known about this species was in this one pubication. The goal of my research was to investigate this snail’s distributional range, habitat use, aspects of its natural history, and its relationship to other Euchemotrema in Oklahoma. I surveyed 106 sites across 15 counties in western Oklahoma searching for E. wichitorum to establish the species’ range and to delimit the range boundary between E. wichitorum and the widespread E. leai aliciae, whose range occurs throughout much of eastern and central Oklahoma. I expanded the species’ known range to from two to seven counties in southwest Oklahoma and analyzed measured habitat characteristics at survey sites in to determine which environmental characters were associated with live abundance of E. wichitorum, finding the species is positively associated with the number or logs in an area and negatively associated with the number of boulders. This, along with other environmental data, suggests the E. wichitorum favors increasingly dense woodlands over the more open, boulder-dominated habitats found within much of its range. I also found that E. wichitorum abundance is positively associated with fire; sites with evidence of relatively recent fire had more live snails and charred logs sheltered more live snails than their unburned counterparts. However, snail mortality is high when fires are severe because shelter habitats are more likely to be burned than during low-severity fires, which leave many unburned patches and often only char the surface of logs rather than the soil-log interface where snails occur. Increased abundance may occur after low-severity fires due to an influx of bioavailable calcium as calcium oxalalate in the leaves and bark of the dominant tree species, Post Oak (Quercus stellata), is converted into soluble calcium ions and calcium carbonate. After locating several populations of Euchemotrema outside the known ranges of E. wichitorum and E. leai that contained individuals of intermediate morphology between the two species, I compared these three groups of snails, along with two other Euchemotrema groups, using a Discriminant Function Analysis in an attempt to classify the intermediate western Oklahoma (“E. westOK”) populations to establish the range boundary between E. wichitorum and E. leai. The DFA using all five Euchemotrema groups did not strongly separate the three focal groups. While a DFA comparing just E. wichitorum and E. leai suggested that E. wichitorum, which had a classification rate of 92%, is morphologically distinct from E. leai, the “E. westOK” populations proved to be morphologically intermediate between the two group and undercuts this initial finding of distinctness. While E. wichitorum appears to have an overall positive conservation outlook, more research is needed understand the evolutionary relationship between this species, E. leai aliciae, and the isolated populations scattered between the ranges of the two species and elsewhere in western Oklahoma.